Method and apparatus for transmitting data by device-to-device terminal in wireless communication system

ABSTRACT

An embodiment of the present invention provides a method for transmitting device-to-device (D2D) data by a terminal in a wireless communication system, the method for transmitting the D2D data comprising the step of: determining a sub-frame pool for transmitting data, which is configured by only sub-frames capable of transmitting and receiving a D2D signal, among multiple sub-frames; determining a set of subframes to transmit D2D data by applying a time resource patter (TRP) to the sub-frame pool for transmitting the data; and transmitting D2D data in the set of the determined sub-frames.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/003534, filed on Apr. 8, 2015,which claims the benefit of U.S. Provisional Application No. 61/977,073,filed on Apr. 8, 2014, the contents of which are all hereby incorporatedby reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting data inDevice-to-Device (D2D) communication.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi-Carrier FrequencyDivision Multiple Access (MC-FDMA) system.

D2D communication is a communication scheme in which a direct link isestablished between User Equipments (UEs) and the UEs exchange voice anddata directly with each other without intervention of an evolved Node B(eNB). D2D communication may cover UE-to-UE communication andpeer-to-peer communication. In addition, D2D communication may find itsapplications in Machine-to-Machine (M2M) communication and Machine TypeCommunication (MTC).

D2D communication is under consideration as a solution to the overheadof an eNB caused by rapidly increasing data traffic. For example, sincedevices exchange data directly with each other without intervention ofan eNB by D2D communication, compared to legacy wireless communication,the overhead of a network may be reduced. Further, it is expected thatwith the introduction of D2D communication will reduce the powerconsumption of devices participating in D2D communication, increase datatransmission rates, increase the accommodation capability of a network,distribute load, and extend cell coverage.

DISCLOSURE OF THE INVENTION Technical Task

A technical task of the present invention is to define data transmissionaccording to a time resource pattern.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of transmitting D2D (device to device) data,which is transmitted by a user equipment in a wireless communicationsystem, includes the steps of determining a subframe pool for datatransmission consisting of only subframes capable of transmitting andreceiving a D2D signal among a plurality of subframes, determining a setof subframes in which D2D data is to be transmitted by applying a TRP(time resource pattern) to the subframe pool for the data transmission,and transmitting D2D data in the determined set of the subframes.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, auser equipment transmitting a D2D (device to device) signal in awireless communication system includes a reception module and aprocessor configured to determine a subframe pool for data transmissionconsisting of only subframes capable of transmitting and receiving a D2Dsignal among a plurality of subframes, the processor configured todetermine a set of subframes in which D2D data is to be transmitted byapplying a TRP (time resource pattern) to the subframe pool for the datatransmission, the processor configured to transmit D2D data in thedetermined set of the subframes.

Embodiments of the present invention can include all or a part of itemsdescribed in the following.

A transport block for the D2D data can be transmitted via thepredetermined number of subframes in the set of the subframes.

The TRP may correspond to a bitmap consisting of bits corresponding toeach of subframes included in the subframe pool for the datatransmission.

A bit configured by 1 among the bits indicates a subframe in which theD2D data is to be transmitted.

A subframe included in the subframe pool for the data transmission and asubframe included in a subframe pool for D2D control information may notbe overlapped with each other.

A plurality of the subframes may be included in a transmission period ofD2D control information.

Information indicating the TRP can be delivered via D2D controlinformation.

Advantageous Effects

According to embodiments of the present invention, it is able tominimize interference/collision between D2D terminals.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a radio frame structure;

FIG. 2 illustrates a structure of a downlink resource grid for theduration of one downlink slot;

FIG. 3 illustrates a structure of a downlink subframe;

FIG. 4 illustrates a structure of an uplink subframe;

FIG. 5 illustrates relay of a synchronization signal;

FIG. 6 illustrates a time resource pattern according to an embodiment ofthe present invention; and

FIG. 7 is a block diagram of a transmission apparatus and a receptionapparatus.

BEST MODE

Mode for Invention

The embodiments described below are constructed by combining elementsand features of the present invention in a predetermined form. Theelements or features may be considered selective unless explicitlymentioned otherwise. Each of the elements or features can be implementedwithout being combined with other elements. In addition, some elementsand/or features may be combined to configure an embodiment of thepresent invention. The sequence of the operations discussed in theembodiments of the present invention may be changed. Some elements orfeatures of one embodiment may also be included in another embodiment,or may be replaced by corresponding elements or features of anotherembodiment.

Embodiments of the present invention will be described, focusing on adata communication relationship between a base station and a terminal.The base station serves as a terminal node of a network over which thebase station directly communicates with the terminal. Specificoperations illustrated as being conducted by the base station in thisspecification may also be conducted by an upper node of the basestation, as necessary.

In other words, it will be obvious that various operations allowing forcommunication with the terminal in a network composed of several networknodes including the base station can be conducted by the base station ornetwork nodes other than the base station. The term “base station (BS)”may be replaced with terms such as “fixed station,” “Node-B,” “eNode-B(eNB),” and “access point”. The term “relay” may be replaced with suchterms as “relay node (RN)” and “relay station (RS)”. The term “terminal”may also be replaced with such terms as “user equipment (UE),” “a mobilestation (MS),” “mobile subscriber station (MSS)” and “subscriber station(SS)”. In the following description, a base station can also be used asa meaning for such a device as a scheduling performing node, a clusterheader or the like. If a base station or a relay transmits a signaltransmitted by a terminal, the base station or the relay can be regardedas a terminal.

The term “cell”, as used herein, may be applied to transmission andreception points such as a base station (eNB), sector, remote radio head(RRH) and relay, and may also be extensively used by a specifictransmission/reception point to distinguish between component carriers.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and these specific terms may bechanged to other formats within the technical scope or spirit of thepresent invention.

In some cases, known structures and devices may be omitted or blockdiagrams illustrating only key functions of the structures and devicesmay be provided, so as not to obscure the concept of the presentinvention. The same reference numbers will be used throughout thisspecification to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an institute of electrical and electronics engineers (IEEE)802 system, a 3rd generation partnership project (3GPP) system, a 3GPPlong term evolution (LTE) system, an LTE-advanced (LTE-A) system, and a3GPP2 system. In particular, steps or parts, which are not described inthe embodiments of the present invention to prevent obscuring thetechnical spirit of the present invention, may be supported by the abovedocuments. All terms used herein may be supported by the above-mentioneddocuments.

The embodiments of the present invention described below can be appliedto a variety of wireless access technologies such as code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), and single carrier frequency division multiple access(SC-FDMA). CDMA may be embodied through wireless technologies such asuniversal terrestrial radio access (UTRA) or CDMA2000. TDMA may beembodied through wireless technologies such as global system for mobilecommunication (GSM)/general packet radio service (GPRS)/enhanced datarates for GSM evolution (EDGE). OFDMA may be embodied through wirelesstechnologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802-20, and evolved UTRA (E-UTRA). UTRA is a part of universal mobiletelecommunications system (UMTS). 3rd generation partnership project(3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS),which uses E-UTRA. 3GPP LTE employs OFDMA for downlink and employsSC-FDMA for uplink. LTE-Advanced (LTE-A) is an evolved version of 3GPPLTE. WiMAX can be explained by IEEE 802.16e (wirelessMAN-OFDMA referencesystem) and advanced IEEE 802.16m (wirelessMAN-OFDMA advanced system).For clarity, the following description focuses on 3GPP LTE and 3GPPLTE-A systems. However, the spirit of the present invention is notlimited thereto.

LTE/LTE-A Resource Structure/Channel

Hereinafter, a radio frame structure will be described with reference toFIG. 1.

In a cellular OFDM wireless packet communication system, an uplink(UL)/downlink (DL) data packet is transmitted on a subframe basis, andone subframe is defined as a predetermined time interval including aplurality of OFDM symbols. 3GPP LTE standard supports a type-1 radioframe structure applicable to frequency division duplex (FDD) and atype-2 radio frame structure applicable to time division duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into ten subframes. Each subframe includes two slots inthe time domain. The time taken to transmit one subframe is defined as atransmission time interval (TTI). For example, a subframe may have aduration of 1 ms and one slot may have a duration of 0.5 ms. A slot mayinclude a plurality of OFDM symbols in the time domain and includes aplurality of resource blocks (RBs) in the frequency domain. Since 3GPPLTE adopts OFDMA for downlink, an OFDM symbol represents one symbolperiod. An OFDM symbol may be referred to as an SC-FDMA symbol or asymbol period. A resource block (RB), which is a resource allocationunit, may include a plurality of consecutive subcarriers in a slot.

The number of OFDM symbols included in one slot depends on theconfiguration of a cyclic prefix (CP). CPs are divided into an extendedCP and a normal CP. For a normal CP configuring each OFDM symbol, a slotmay include 7 OFDM symbols. For an extended CP configuring each OFDMsymbol, the duration of each OFDM symbol extends and thus the number ofOFDM symbols included in a slot is smaller than in the case of thenormal CP. For the extended CP, a slot may include, for example, 6 OFDMsymbols. When a channel status is unstable as in the case of high speedmovement of a UE, the extended CP may be used to reduce inter-symbolinterference.

When the normal CP is used, each slot includes 7 OFDM symbols, and thuseach subframe includes 14 OFDM symbols. In this case, the first two orthree OFDM symbols of each subframe may be allocated to a physicaldownlink control channel (PDCCH) and the other three OFDM symbols may beallocated to a physical downlink shared channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. The type-2 radioframe includes two half frames, each of which has 5 subframes, adownlink pilot time slot (DwPTS), a guard period (GP), and an uplinkpilot time slot (UpPTS). Each subframe includes two slots. The DwPTS isused for initial cell search, synchronization, or channel estimation ina UE, whereas the UpPTS is used for channel estimation in an eNB and ULtransmission synchronization in a UE. The GP is provided to eliminateinterference taking place in UL due to multipath delay of a DL signalbetween DL and UL. Regardless of the type of a radio frame, a subframeof the radio frame includes two slots.

Herein, the illustrated radio frame structures are merely examples, andvarious modifications may be made to the number of subframes included ina radio frame, the number of slots included in a subframe, or the numberof symbols included in a slot.

FIG. 2 is a diagram illustrating a resource grid for one DL slot. A DLslot includes 7 OFDM symbols in the time domain and an RB includes 12subcarriers in the frequency domain. However, embodiments of the presentinvention are not limited thereto. For a normal CP, a slot may include 7OFDM symbols. For an extended CP, a slot may include 6 OFDM symbols.Each element in the resource grid is referred to as a resource element(RE). An RB includes 12 7 REs. The number NDL of RBs included in adownlink slot depends on a DL transmission bandwidth. A UL slot may havethe same structure as a DL slot.

FIG. 3 illustrates a DL subframe structure. Up to the first three OFDMsymbols of the first slot in a DL subframe used as a control region towhich control channels are allocated and the other OFDM symbols of theDL subframe are used as a data region to which a PDSCH is allocated. DLcontrol channels used in 3GPP LTE include, for example, a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), and a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH). The PCFICH is transmitted at the first OFDMsymbol of a subframe, carrying information about the number of OFDMsymbols used for transmission of control channels in the subframe. ThePHICH carries a HARQ ACK/NACK signal in response to uplink transmission.Control information carried on the PDCCH is called downlink controlinformation (DCI). The DCI includes UL or DL scheduling information orUL transmission power control commands for UE groups. The PDCCH deliversinformation about resource allocation and a transport format for a DLshared channel (DL-SCH), resource allocation information about an ULshared channel (UL-SCH), paging information of a paging channel (PCH),system information on the DL-SCH, information about resource allocationfor a higher-layer control message such as a random access responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, and voice over internet protocol (VoIP) activationinformation. A plurality of PDCCHs may be transmitted in the controlregion. A UE may monitor a plurality of PDCCHs. A PDCCH is formed byaggregating one or more consecutive control channel elements (CCEs). ACCE is a logical allocation unit used to provide a PDCCH at a codingrate based on the state of a radio channel. A CCE corresponds to aplurality of RE groups. The format of a PDCCH and the number ofavailable bits for the PDCCH are determined depending on the correlationbetween the number of CCEs and a coding rate provided by the CCEs. AneNB determines the PDCCH format according to DCI transmitted to a UE andadds a cyclic redundancy check (CRC) to the control information. The CRCis masked by an identifier (ID) known as a radio network temporaryidentifier (RNTI) according to the owner or usage of the PDCCH. If thePDCCH is directed to a specific UE, its CRC may be masked by a cell-RNTI(C-RNTI) of the UE. If the PDCCH is for a paging message, the CRC of thePDCCH may be masked by a paging indicator identifier (P-RNTI). If thePDCCH delivers system information, particularly, a system informationblock (SIB), the CRC thereof may be masked by a system information IDand a system information RNTI (SI-RNTI). To indicate that the PDCCHdelivers a random access response in response to a random accesspreamble transmitted by a UE, the CRC thereof may be masked by a randomaccess-RNTI (RA-RNTI).

FIG. 4 illustrates a UL subframe structure. A UL subframe may be dividedinto a control region and a data region in the frequency domain Aphysical uplink control channel (PUCCH) carrying uplink controlinformation is allocated to the control region and a physical uplinkshared channel (PUSCH) carrying user data is allocated to the dataregion. To maintain single carrier property, a UE does notsimultaneously transmit a PUSCH and a PUCCH. A PUCCH for a UE isallocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. This is often called frequencyhopping of the RB pair allocated to the PUCCH over a slot boundary.

Synchronization Acquisition of D2D UE

Now, a description will be given of synchronization acquisition betweenUEs in D2D communication based on the foregoing description in thecontext of the legacy LTE/LTE-A system. In an OFDM system, iftime/frequency synchronization is not acquired, the resulting Inter-CellInterference (ICI) may make it impossible to multiplex different UEs inan OFDM signal. If each individual D2D UE acquires synchronization bytransmitting and receiving a synchronization signal directly, this isinefficient. In a distributed node system such as a D2D communicationsystem, therefore, a specific node may transmit a representativesynchronization signal and the other UEs may acquire synchronizationusing the representative synchronization signal. In other words, somenodes (which may be an eNB, a UE, and a Synchronization Reference Node(SRN, also referred to as a synchronization source)) may transmit a D2DSynchronization Signal (D2DSS) and the remaining UEs may transmit andreceive signals in synchronization with the D2DSS.

D2DSSs may include a Primary D2DSS (PD2DSS) or a Primary SidelinkSynchronization Signal (PSSS) and a Secondary D2DSS (SD2DSS) or aSecondary Sidelink Synchronization Signal (SSSS). The PD2DSS may beconfigured to have a similar/modified/repeated structure of a Zadoff-chusequence of a predetermined length or a Primary Synchronization Signal(PSS), and the SD2DSS may be configured to have asimilar/modified/repeated structure of an M-sequence or a SecondarySynchronization Signal (SSS). If UEs synchronize their timing with aneNB, the eNB serves as an SRN and the D2DSS is a PSS/SSS. A Physical D2DSynchronization Channel (PD2DSCH) may be a (broadcast) channel carryingbasic (system) information that a UE should first obtain before D2Dsignal transmission and reception (e.g., D2DSS-related information, aDuplex Mode (DM), a TDD UL/DL configuration, a resource pool-relatedinformation, the type of an application related to the D2DSS, etc.). ThePD2DSCH may be transmitted in the same subframe as the D2DSS or in asubframe subsequent to the frame carrying the D2DSS.

The SRN may be a node that transmits a D2DSS and a PD2DSCH. The D2DSSmay be a specific sequence and the PD2DSCH may be a sequencerepresenting specific information or a codeword produced bypredetermined channel coding. The SRN may be an eNB or a specific D2DUE. In the case of partial network coverage or out of network coverage,the SRN may be a UE.

In a situation illustrated in FIG. 5, a D2DSS may be relayed for D2Dcommunication with an out-of-coverage UE. The D2DSS may be relayed overmultiple hops. The following description is given with the appreciationthat relay of an SS covers transmission of a D2DSS in a separate formataccording to a SS reception time as well as direct Amplify-and-Forward(AF)-relay of an SS transmitted by an eNB. As the D2DSS is relayed, anin-coverage UE may communicate directly with an out-of-coverage UE. FIG.5 illustrates an exemplary case in which a D2DSS is relayed andcommunication is conducted between D2D UEs based on the relayed D2DSS.

A Time Resource Pattern (TRP) for use in transmitting data, a discoverysignal, etc. by a UE will be described according to various embodimentsof the present invention. The term ‘TRP’ may be interchangeably usedwith ‘Resource Pattern for Transmission (RPT)’ or ‘Time-RPT (T-RPT)’.However, the terms should not be construed as limiting the scope of thepresent invention. Thus, it is clarified that a resource pattern havingTRP properties as described below corresponds to a TRP. In the followingdescription, a scheme for indicating the position of transmissionresources by an eNB/UE is referred to as mode 1/type 2 and a scheme forindicating the position of transmission resources in a specific resourcepool by a transmitting UE (by the UE's selection) is referred to as mode2/type 1. In the following description, Scheduling Assignment (SA) maymean control information related to D2D data transmission and a channelcarrying the control information. Before data transmission, an SA mayfirst be transmitted. A receiving D2D UE may determine the position ofresources carrying the data by decoding the SA and then receive a D2Dsignal in the resources. In the following description, D2D may bereferred to as sidelink. For the convenience of description, the term‘TRP indication bit sequence’ may be used. The TRP indication bitsequence may include only an ID included in an SA. If the SA includes anadditional bit field indicating a TRP, the TRP indication bit sequencemay be interpreted as ID+TRP bit sequence. Or a bit sequence forindicating a TRP independent of the ID may be included in the SA. Inthis case, the TRP bit sequence may be interpreted as the TRP indicationbit sequence. A set of bit sequences used to indicate a TRP, includedand transmitted in the SA may be interpreted as the TRP indication bitsequence.

TRP

FIG. 6 illustrates TRPs according to an embodiment of the presentinvention. Referring to FIG. 6, a plurality of subframes 601 may includesubframes available for D2D signal transmission and reception (e.g., ULsubframes in TDD, and D2D communication subframes in FIG. 6) andsubframes unavailable for D2D signal transmission and reception (non-D2Dcommunication subframes in FIG. 6). The plurality of subframes 601 maybe included within a D2D control information transmission period (e.g.,a physical sidelink control channel). A subframe pool 602 for datatransmission may be determined, which includes only D2D communicationsubframes from among the plurality of subframes 601.

As TRPs (TRP #0, #1, . . .) are applied to the subframe pool 602 fordata transmission, a set of subframes to transmit D2D data may bedetermined. For example, if TRP #1 is applied to the subframe pool 602for data transmission, an 8^(th) subframe and 10^(th) to 16^(th)subframes may be included in a subframe set, for D2D data transmission.Shaded parts of the TRPs in FIG. 16 may indicate subframes that willcarry D2D data. A TRP may be a bitmap having bits corresponding to therespective subframes of a subframe pool for data transmission. If a bitof the bitmap is set to 1, the bit may indicate a subframe to transmitD2D data. Specifically, if a TRP is configured to be a bitmap, theshaded parts of the TRP may be 1 s and the non-shaded parts of the TRPmay be 0 s in FIG. 6. For example, TRP #1 is a bitmap of {0, 0, 0, 0, 0,0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1}.

Once a subframe set is determined for transmission of D2D data, the D2Ddata may be transmitted in the subframe set. Upon receipt of an SA, a UEmay detect and decode a D2D signal in corresponding subframes, expectingtransmission of the D2D signal in the subframes.

In the above description, a Transport Block (TB) for D2D data may betransmitted in a predetermined number of subframes in a subframe set.That is, the number of repetitions/a retransmission number/the number ofretransmissions may be predetermined for each TB. For example, thenumber of retransmissions per TB may be fixed to 4.

The above-described plurality of subframes may be contiguous subframesfollowing D2D control information-related subframes (including ULsubframes that may carry D2D control information, DL subframes with norelation to the UL subframes, and special subframes in TDD) in one D2Dcontrol information period (i.e., one SA period). The D2D controlinformation (an SA, an MCS, resource allocation information, a TRP,etc.) may be transmitted in subframes determined to transmit D2D controlinformation (i.e., a subframe pool (for D2D control information)) fromamong subframes available for transmission of D2D control informationaccording to an SA subframe bitmap. In this case, information indicatinga TRP in a subframe next to the subframe pool for D2D controlinformation may be transmitted in the D2D control information. If one SAperiod is configured as described above, subframes included in asubframe pool for data transmission are not overlapped with subframesincluded in a subframe pool for D2D control information. Morespecifically, if the subframe pool for D2D control information isoverlapped with the subframe pool for D2D data transmission, it may beregulated that D2D control information or D2D data is always transmittedand the D2D control information and the D2D data are not transmitted inthe same subframe.

Meanwhile, the subframe pool for data transmission may not be definedseparately in D2D communication mode 1. In this case, UL subframesfollowing the subframe pool for D2D control information transmission(specifically, a subframe pool including the first subframe of asubframe bitmap for D2D control information transmission to a subframecorresponding to the last 1 of the bitmap) may be a subframe pool forimplicit mode 1 D2D data transmission.

Application of TRP

In the foregoing description, a TRP may be applied to subframes asfollows.

A UE may determine a subframe indicator bitmap corresponding to TRPindication information. If the UE is a D2D control informationtransmitter, the TRP indication information may be transmitted in D2Dcontrol information. If the UE is a D2D control information receiver,the TRP indication information may be included in received D2D controlinformation. Herein, the TRP indication information may be described ina later-described TRP indication part or may be an index indicating aspecific subframe indicator bitmap. For example, if the size of thesubframe indicator bitmap is 8, there may be a set of available bitmaps.An index may be assigned to each bitmap included in the bitmap set and asubframe indicator bitmap may be determined by such as index.

A bitmap to be applied to a subframe pool for data transmission may bedetermined from the subframe indicator bitmap. The subframe indicatorbitmap may be smaller than the subframe pool for data transmission insize. In this case, the subframe indicator bitmap (e.g., a TRPindication bit sequence) may be repeated. If the length of the TRPindication bit sequence is M, the M-bit sequence is simply repeated andfilled in the remaining L subframes. If L is not a multiple of M, a TRPmay be generated by sequentially filling the remaining bit sequence inthe L subframes.

That is, if the subframe indicator bitmap is smaller in size than thesubframe pool for data transmission, the subframe indicator bitmap maybe repeated within the bitmap for the subframe pool for datatransmission.

For example, if the size M of the subframe indicator bitmap is smallerthan the number of subframes in the resource pool for data transmissionand the UE transmits D2D data in the first subframe of the subframe poolfor data transmission, the UE may transmit D2D data in a (1+M)^(th)subframe of the subframe pool. Or a first bit value of the bitmap (to beapplied to the subframe pool for data transmission) may be equal to a(subframe indicator bitmap size+1)^(th) bit value.

If the size of the subframe pool for data transmission is not a multipleof the size of the subframe indicator bitmap, the bits of the lastrepeated subframe indicator bitmap may be used sequentially. In otherwords, if the size of the subframe pool for data transmission is not amultiple of the size of the subframe indicator bitmap, the last repeatedsubframe indicator bitmap may be truncated. Specifically, if thesubframe indicator bitmap is 16 bits {0, 0, 0, 0, 0, 0, 0, 1,0, 1, 1, 1,1, 1, 1, 1} and the subframe pool includes 36 subframes, the bitmap (tobe applied to a subframe pool for data transmission) is configured byrepeating the subframe indicator bitmap twice and using the first 4 bitsof the subframe indicator bitmap sequentially at the third repetition(while truncating the remaining bits). That is, the bitmap (to beapplied to the subframe pool for data transmission) is {0, 0, 0, 0, 0,0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1,1, 1, 1, 0, 0, 0, 0}.

Indication of TRP

Now, a description will be given of a method for indicating theabove-described TRP.

First, an eNB may indicate an ID and TRP bits included and transmittedin an SA by a D2D SA grant in mode 1. The ID sequence included in the SAand/or the sequence of a TRP bit field included in the SA (a bit fieldindicating a specific ID and/or a TRP) may be explicitly included in theD2D SA grant. Or the ID sequence to be transmitted in the SA and/or theTRP bit field to be transmitted in the SA may be generated by hashingthe bit sequence of a D2D-RNTI or using partial bits (e.g., lower Nbits) of the bit sequence of the D2D-RNTI. Because an RNTI is differentfor each UE and at least a part of the RNTI is used, the position of D2Dresources may be configured for each UE without additional signaling. AD2D-RNTI is an ID pre-signaled to distinguish D2D control informationfrom other control information and is used for masking the CRC of theD2D control information. A part of the ID included and transmitted inthe SA may be generated from the RNTI and the remaining part of the IDmay be generated based on a target ID (or a group ID). Or the ID may begenerated by combining (e.g., AND/XOR/OR-operating) both the RNTI andthe target or group ID. The ID included and transmitted in the SA may bechanged over time. Characteristically, only a Transmission (Tx) UE IDmay be changed. This is because if up to a target UE ID part is hoppedand a target UE is not aware of the hopping, the target UE may notdetect the ID. If the target UE is aware of even a hopping pattern ofthe target UE ID part, every ID sequence included in the SA may behopped in a predetermined rule. The changeability (hopping) of the IDsequence over time may be implemented by directly setting a differentbit field in a D2D SA grant by the eNB and the ID sequence may bechanged in a predetermined rule after the D2D SA grant of the eNB. Forexample, the ID sequence included in the D2D SA grant may be used as aninitialization parameter for a random sequence and a time-variantsequence may be generated using a random sequence created using theinitialization parameter.

Second, an ID may be transmitted in an SA and a TRP may be determinedusing the ID in mode 2. The ID may be a short ID induced from an ID (atransmission and/or reception (target or group) ID) by a higher layer ora bit sequence used to configure the transmission position of data and ascrambling parameter. If the ID included in the SA is too short forcreation of TRP candidates, the probability of collision between IDs isincreased. In this case, a plurality of Tx UEs are likely to use thesame TRP. To prevent this, a part of the bits of the SA may include bitsindicating a TRP. Also, a specific TRP may be indicated by combining anID bit field and bits of a TRP field in the SA. For example, the IDincluded in the SA may be used to indicate a TRP set and TRP indicationbits included in the SA may indicate a specific index within the TRPset. In another example, the TRP bits included in the SA may indicate aspecific TRP set within a resource pool and the ID included in the SAmay indicate a specific TRP within the pool/set indicated by the TRPbits. In this case, the bits indicating a TRP set may be transmittedsemi-statically without being transmitted in every SA. For example, thebits indicating a TRP set may be used as a virtual CRC on the assumptionthat the bits are transmitted in every n^(th) SA or even though the bitsare transmitted in every SA, they are not changed over n SAtransmissions. Meanwhile, these TRP bits are not included additionally.Rather, the TRP bits may be transmitted by borrowing an unused state ofMCS bits or any other SA bit field. Or a TRP pattern may be indicated byusing all unused states of additionally included bits and other bitfields.

Meanwhile, the size of TRP bits used in an indication of an SA may bechanged according to the size of a D2D UE group or the number of Tx UEsin the group. For example, if a specific police officer group includes Npolice officers, the number of TRP indication bits is set to log2(N).Herein, the remaining unused bits may be used for other purposes or maybe set to Os for use as a virtual CRC.

Meanwhile, an ID may be set differently for a TRP in mode 1 and mode 2.For example, while a TRP may be indicated using only a Tx UE ID in mode1, a TRP may be indicated using both a Tx UE ID and a target UE ID(group ID) in mode 2.

To configure a TRP, the following information may be used: i)information about the size of a transmission opportunity from theviewpoint of a UE (this information indicates how many resources areallocated to one UE by one SA); and ii) information about the number ofretransmissions for each TB (this information may be information aboutthe number of TB s transmitted during one SA period. In this case, thenumber of retransmissions for each TB may be calculated by flooring thesize (number) of transmission opportunities during one SA period/thenumber of TBs transmitted by one SA. Or this information may beinformation about the (maximum) number of repetitions for each TB). Partof the information may be preset or configured by the network. Theinformation may be preset for an out-of-coverage UE or signaled to theout-of-coverage UE from another UE within the network by aphysical-layer signal or a higher-layer signal. In addition, part of theinformation may be included and transmitted in an SA. For example, thetransmission opportunity size may be preset or configured by thenetwork. Herein, a retransmission number for each TB may be included andtransmitted in the SA. On the other hand, information about thetransmission opportunity size may be included and transmitted in the SAand information about the retransmission number may be preset orsemi-statically indicated in a higher-layer signal by the network.

In a specific example, if an SA includes an 8-bit ID, the number of TRPsdistinguishable by IDs is 256 (=2^8). If a mode-2 resource pool includes16 subframes and a transmission opportunity size is 8, the number ofTRPs that can be generated is 12870 (=16C8). Therefore, it is impossibleto identify a TRP only by the ID bits included in the SA. To avoid thisproblem, additional bits may be included in the SA in order to indicatea TRP in the above-described method. In this case, about 6 additionalbits are needed to distinguish all TRPs that can be produced. Theadditional bits may be available from a combination of unused MCS statesand a new bit field or from an additional bit field.

Configurations of Apparatuses According to Embodiment of the PresentInvention

FIG. 7 is a block diagram of a transmission point and a UE according toan embodiment of the present invention.

Referring to FIG. 7, a transmission point 10 according to the presentinvention may include a Reception (Rx) module 11, a Tx module 12, aprocessor 13, a memory 14, and a plurality of antennas 15. Use of theplurality of antennas 15 means that the transmission point 10 supportsMIMO transmission and reception. The reception module 11 may receive ULsignals, data, and information from a UE. The Tx module 12 may transmitDL signals, data, and information to a UE. The processor 13 may provideoverall control to the transmission point 10.

The processor 13 of the transmission point 10 according to theembodiment of the present invention may perform necessary operations inthe afore-described embodiments.

Besides, the processor 13 of the transmission point 10 processesreceived information and information to be transmitted to the outside ofthe transmission point 10. The memory 14 may store the processedinformation for a predetermined time and may be replaced with acomponent such as a buffer (not shown).

Referring to FIG. 7 again, a UE 20 according to the present inventionmay include an Rx module 21, a Tx module 22, a processor 23, a memory24, and a plurality of antennas 25. Use of the plurality of antennas 25means that the UE 20 supports MIMO transmission and reception using theplurality of antennas 25. The Rx module 21 may receive DL signals, data,and information from an eNB. The Tx module 22 may transmit UL signals,data, and information to an eNB. The processor 23 may provide overallcontrol to the UE 20.

The processor 23 of the UE 20 according to the embodiment of the presentinvention may perform necessary operations in the afore-describedembodiments.

Besides, the processor 23 of the UE 20 processes received informationand information to be transmitted to the outside of the UE 20. Thememory 24 may store the processed information for a predetermined timeand may be replaced with a component such as a buffer (not shown).

The above transmission point and UE may be configured in such a mannerthat the above-described various embodiments of the present inventionmay be implemented independently or in combination of two or more. Aredundant description is omitted for clarity.

The description of the transmission point 10 in FIG. 7 is applicable toa relay as a DL transmitter or a UL receiver, and the description of theUE 20 in FIG. 7 is applicable to a relay as a DL receiver or a ULtransmitter.

The embodiments of the present invention may be implemented by variousmeans, for example, in hardware, firmware, software, or a combinationthereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

The detailed description of the preferred embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. Accordingly, the inventionshould not be limited to the specific embodiments described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentinvention or included as a new claim by a subsequent amendment after theapplication is filed.

INDUSTRIAL APPLICABILITY

The above-described embodiments of the present invention are applicableto various mobile communication systems.

What is claimed is:
 1. A method of transmitting D2D (device to device)data, which is transmitted by a user equipment in a wirelesscommunication system, comprising: determining, by a D2D UE, a subframepool for transmission of the D2D data including only subframes capableof transmitting and receiving a D2D signal among a plurality ofsubframes including D2D available subframes and D2D unavailablesubframes; determining, by a D2D UE, a set of subframes in which the D2Ddata is to be transmitted from the subframe pool for the transmission ofthe D2D data based on a subframe indicator bitmap, wherein the subframeindicator bitmap is repeatedly used for the determined set of thesubframes; and transmitting the D2D data in the determined set of thesubframes.
 2. The method of claim 1, wherein a transport block for theD2D data is transmitted via a predetermined number of subframes in theset of the subframes.
 3. The method of claim 1, wherein the subframeindicator bitmap includes bits corresponding to each of subframesincluded in the subframe pool for the transmission of the D2D data. 4.The method of claim 1, wherein a bit configured by 1 among bits in thesubframe indicator bitmap indicates a subframe in which the D2D data isto be transmitted.
 5. The method of claim 1, wherein a subframe includedin the subframe pool for the transmission of the D2D data and a subframeincluded in a subframe pool for D2D control information are notoverlapped with each other.
 6. The method of claim 1, wherein aplurality of the subframes are included in a transmission period of D2Dcontrol information.
 7. The method of claim 1, wherein informationindicating the subframe indicator bitmap is delivered via D2D controlinformation.
 8. A user equipment transmitting a D2D (device to device)signal in a wireless communication system, comprising: a receptionmodule; and a processor configured to determine a subframe pool fortransmission of D2D data including only subframes capable oftransmitting and receiving the D2D signal among a plurality of subframesincluding D2D available subframes and D2D unavailable subframes, theprocessor configured to determine a set of subframes in which the D2Ddata is to be transmitted from the subframe pool for the transmission ofthe D2D data based on a subframe indicator bitmap, wherein the subframeindicator bitmap is repeatedly used for the determined set of thesubframes, and the processor is further configured to transmit the D2Ddata based on the set of the subframes.
 9. The user equipment of claim8, wherein a transport block for the D2D data is transmitted via apredetermined number of subframes in the set of the subframes.
 10. Theuser equipment of claim 8, wherein the subframe indicator bitmapincludes bits corresponding to each of subframes included in thesubframe pool for transmission of the D2D data.
 11. The user equipmentof claim 8, wherein a bit configured by 1among bits in the subframeindicator bitmap indicates a subframe in which the D2D data is to betransmitted.
 12. The user equipment of claim 8, wherein a subframeincluded in the subframe pool for transmission of the D2D data and asubframe included in a subframe pool for D2D control information are notoverlapped with each other.
 13. The user equipment of claim 8, wherein aplurality of the subframes are included in a transmission period of D2Dcontrol information.
 14. The user equipment of claim 8, whereininformation indicating the subframe indicator bitmap is delivered viaD2D control information.